1. Field of the Invention
The present invention relates to a crosslinkable sulfonated copolymer and a fuel cell including a polymeric composition of the same.
2. Description of the Related Art
Fuel cells are electrochemical devices which directly transform chemical energy between hydrogen and oxygen which are contained in hydrocarbon materials such as methanol, ethanol, and natural gas into electrical energy. The energy transformation process of fuel cells is very efficient and environmentally-friendly, thereby drawing attention for the past few years.
Fuel cells can be classified into Phosphoric Acid Fuel Cells (PAFC), Molten Carbonate Fuel Cells (MCFC), Solid Oxide Full Cells (SOFC), Polymer Electrolyte Membrane Fuel Cells (PEMFC), and Alkaline Full Cells (AFC) according to the type of electrolyte used. All fuel cells operate on the same principle, but the type of fuel used, operating speed, the catalyst used, and the electrolyte used are different. In particular, PEMFCs are capable of being used in small-sized stationary power generation equipment or transportation systems due to their high reaction speed, low operating temperature, high output density, rapid start-up, and output request variation.
The core part of a PEMFC is a Membrane and Electrode Assembly (MEA). A MEA comprises a polymer electrolyte membrane and two electrodes on either side of the polymer electrolyte membrane, which independently act as a cathode and an anode.
The polymer electrolyte membrane acts as a separator, blocking direct contact between an oxidizing agent and a reducing agent, and electrically insulates the two electrodes while conducting protons. Accordingly, a good polymer electrolyte membrane has high proton conductivity, good electrical insulation, low reactant permeability, excellent thermal, chemical and mechanical stability under normal fuel cell conditions, and a reasonable price.
In order to meet these requirements, various types of polymer electrolyte membranes have been developed, and, in particular, a highly fluorinated polysulfonic acid membranes such as a NAFION™ membrane, have been developed due to their excellent durability and performance. However, a NAFION™ membrane needs to be sufficiently moisturized and used at 80° C. or less to prevent moisture loss.
Moreover, in a Direct Methanol Fuel Cell (DMFC), an aqueous methanol solution is supplied as a fuel to the anode and a portion of non-reactive aqueous methanol solution is permeated to the polymer electrolyte membrane. The non-reactive aqueous methanol solution that permeates to the polymer electrolyte membrane causes a swelling phenomenon in the polymer electrolyte membrane, and the swelling is diffused affecting a cathode catalyst layer. Such a phenomenon is referred to as ‘methanol crossover’, that is, the direct oxidization of methanol at the cathode where an electrochemical reduction of hydrogen ions and oxygen occurs, and thus a methanol crossover results in a drop in electric potential, thus causing a decline in the performance of the DMFC.
This issue is common in other fuel cells using a liquid fuel such as a polar organic fuel.